devfreq: devfreq_simple_dev: call clk_round_rate in dev_target

clk_set_rate is failing for some of the frequencies due to higher
precision introduced in clock driver. Hence call the clk_round_rate
again in dev_target to make sure we send the correct frequency to
clk_set_rate.

Change-Id: I3e40690bf794d99debbcecdcaf05aaac3363caa8
Signed-off-by: Hanumath Prasad <hpprasad@codeaurora.org>